Calutron ion source having a movable baffle for improving the ion output



May 7, 1968 J. v. LEE 3,382,359

CALUTRON ION SOURCE HAVING A MOVABLE BAFFLE FOR IMPROVING THE ION OUTPUT Filed July 8, 1965 0 O 4 o o o -o Fig. 1.

g 1\ Z i 9 11 t Q1 1' 1 $1 T0 OSCILLOSCOPE Fig. 2.

INVENTOR.

John V. Lee BY ATTORNEY.

United States Patent 3,382,359 CALUTRON ION SOURCE HAVING A MOVABLE BAFFLE FOR IMPROVING THE ION OUTPUT John V. Lee, Oak Ridge, Tenn., assignor to the United States of America as represented by the United States Atomic Energy Commission Filed July 8, 1965, Ser. No. 470,651 7 Claims. (Cl. 250-419) ABSTRACT OF THE DISCLOSURE A perforated movable bafile is utilized within the ionization chamber of a calutron ion source and means are provided for adjusting the position of the bafile such that signals derived from the baffle, as viewed on an oscilloscope, indicate a minimum in the amplitudes of oscillations when the bafiie has been positioned properly which results in a maximum ion output.

It has been shown that isotopes of many chemical elements can be separated and the desired elements enriched in the electromagnetic mass spectrometer known as the calutron, described in the E. 0. Lawrence Patent No. 2,709,222. In the calutron, described in that patent, there is provided an ion-producing means wherein a feed or charge material is converted into ions for subsequent acceleration through a magnetic field and separation into the respective masses of the isotopes present in the charge material. Since many charge materials are solids, the charge must first be heated in a vaporizer or oven to produce a charge vapor. Vapor from the vaporizer or even passes to an arc chamber wherein a stream of electrons (commonly called the arc discharge) is passed though these vapors, ionizing them for subsequent acceleration through a magnetic field. One means for heating the charge material for use in an ion source is disclosed in US. Patent No. 3,115,575 to William A. Bell et al., issued Dec. 24, 1963.

It has long been apparent that the process of removing (extracting) ions from the arc column in a calutron ion source is rather ineflicient and subject to many operating conditions. Throughout the many years of calutron development, numerous changes have been made, or tested, to enhance the extraction, e.g., shaping of accelerating electrodes, shaping and repositioning of electron defining slots, use of a floating anode, etc. With each of these generally optimized, the conditions of feed rate, are voltage, etc., still are the controlling factors in optimizing ion output. In addition to the problem of low efiiciency, there has existed .a problem of ion beam oscillation. One of the predominant factors that cause ion beam instabilities or oscillations and result in the contamination of isotopically separated material at the calutron receiver has been determined, as a result of studies, to be ion oscillations at the ion source. These are less evident if the source is operated at lower outputs which, of course, greatly reduces the efliciency of the separation process. Thus, there exists a need for some means for substantially reducing these oscillations while providing for more efficient operation.

With a knowledge of the limitations of prior ion sources for use in calutrons, it is a primary object of the present invention to provide an improved means and method for operating an ion source wherein the objectionable oscillations occurring therein are minimized.

It is another object of the present invention to provide a means and method for operating an ion source as in the preceding object wherein the charge material feed to the source can be increased, thus resulting in more efiicient operation when used in a calutron.

3,382,359 Patented May 7, 1968 ice These and other objects and advantages of the present invention will become apparent upon a consideration of the following detailed specification and the accompanying drawings, wherein:

FIG. 1 is an isometric drawing of the ionization chamber of a calutron ion source of the present invention,

FIG. 2 is a cross sectional view of the ionization chamber of FIG. 1, and

FIGS. 3a-3e show the various types of bafiies that may be used within the ionization chamber of FIG. 2.

The above objects have been accomplished in the present invention by the use of a movable baffle within the ionization chamber of an ion source with means for adjusting the position thereof such that signals derived from the bafiie, as viewed on an oscilloscope, indicate a minimum in the amplitude of oscillation when the baffle has been positioned properly which results in a maximum ion output.

Referring now to FIG. 1 and FIG. 2 of the drawings, a conventional arc chamber 1 is provided with conventional electron defining (collimation) slots 2, 3 at each end thereof. A filament 4 is placed adjacent to slot 2 and a floating anode, or a second filament 5, is placed adjacent to slot 3. Other conventional components have been eliminated from the drawing for clarity except, in FIG. 2, an ion exit defining cover 10 is shown. Positioned within the chamber 1 is a baffle 6 extending a substantial portion of the length and height of the chamber. The battle 6, which may have a cross section of any of the types shown in FIGS. 3-a 3e, contains a plurality of perforations 7 and. is attached to a movable push rod 8 extending through the back of the chamber. The rod 8 is insulated from the chamber 1 by an insulator 9 to permit monitoring signals received on the bafile by means of an oscilloscope over lead 11, or to apply any desired D.C. or A.C. (R.F.) potential thereto. In the case of the bafiie shown in FIG. 30, the central portion is maintained at the positive (M) potential of the source while a separate potential may be applied to the outer portions. In some operations of the ion source, the selected baffie may be left either electrically floating or be grounded, once the optimum position of the bafile has been determined.

In operation of the present ion source, an arc discharge is established between the filament 4 and anode 5, and a vapor of charge material or a gaseous-type feed is fed into a manifold region 12 of the ion source of FIG. 2 from a vaporizer or oven or gas source, not shown, in a conventional manner. Vapor or gas passes from the region 12 into the arc region 13 of the ion source through the openings 7 in the bafile 6 and the vapor or gas is ionized by the arc discharge. The ions formed are then withdrawn from the region 13 through the opening in the exit cover 10 and are accelerated by conventional electrical potentials through a magnetic field to suitable ion receivers in a conventional manner, as set forth in the above-mentioned Lawrence patent. When vapor is fed into the manifold region 12, it may be from a remote vaporizer or oven or from a unit mounted adjacent to the arc chamber 1. In the latter case, the means for moving the bafile 6 can be modified in any suitable fashion to make room for the adjacent oven. When the device of the present invention is used with gaseous-type feeds or vapor from a remote oven, the bafile 6 is moved by the means shown in FIG. 2.

The shape of the bafile is not critical and the various baffle shapes as shown in FIGS. Zia-3e are only by way of example of those that can be used. All of these baffles function approximately in the same fashion.

In all tests of the ion source of the present invention, the ion output was found to be a function of bafiie position with a rather sharply observed optimum position.

Signals derived from the bafiie, as viewed on an oscilloscope, indicated a minimum in the amplitudes of oscillations when the bafile was positioned properly for maximum ion output. Corresponding decreases in the amplitudes of oscillations at the calutron receiver were also observed when the baffle was correctly positioned.

The use of a movable bafile provides for a useful calutron ion source control. For example, several tests were performed wherein the calutron operation was optimized as to ion output and isotopic separation with normal contr-ols while the baffie was completely withdrawn. In nearly all instances, an advanced position of the baffle to an optimum position where the amplitudes of oscillations were a minimum brought about improved stability and permitted a higher feed rate of charge material into the arc chamber with a significant increase in ion output while maintaining the desired degree of isotopic separation. In some instances, outputs nearly double those of normal operation have been achieved. Thus, it should be evident that the use of a movable baffie provides a fine tuning control for are conditions by reducing the amplitudes of oscillations and permitting increased arc density.

This invention has been described by way of illustration rather than by way of limitation and it should be apparent that the invention is equally applicable in fields other than those described.

What is claimed is:

1. A method for improving the ion output of an ion source of a calutron unit comprising the steps of initiating an arc discharge within said ion source; feeding charge material vapor to the arc chamber of said source at a normal, first predetermined rate for ionization by said discharge; moving a perforated baffle within said are chamber; measuring the amplitudes of oscillating signals from said baflle as it is being moved and terminating movement of said baffle when the amplitudes of said signals are at a minimum, thus minimizing the efiects of oscillations occurring within said chamber; and increasing the feed rate of said vapor to a second, higher rate thereby increasing the ion output of said source to a value substantially greater than that achieved with said normal feed rate.

2. A method for improving the ion output of an ion source of a calutron unit, said source including an arc chamber region separated from a manifold region by a perforated bafiie; comprising the steps of initiating an arc discharge within the arc chamber region of said source; feeding charge material to the manifold region of said source at a normal, first predetermined rate, said charge material passing from said manifold region to said arc chamber region through said baffle and into the path of said are discharge where it is ionized; moving said baffie within said source; measuring the amplitudes of oscillating signals from said baffle as it is being moved and terminating movement of said bafile when the amplitudes of said signals are at a minimum, thus minimizing the effects of oscillations occurring within said are chamber region; and increasing the feed rate of said charge material to a second, higher rate thereby increasing the ion output of said source up to a value greater than that achieved with said normal feed rate.

3. The method set forth in claim 2, wherein said charge material is vaporized in an oven before being fed to said manifold region of said source.

4. The method set forth in claim 2, wherein the charge material fed to said manifold region of said source is a gas.

5. A method for improving the operation of an ion source of a calutron unit comprising the steps of initiating an arc discharge within the arc chamber of said ion source; feeding charge material vapor into said are discharge; moving a perforated baflie within said are chamber in relationship to the spacing between said bafiie and said are discharge; measuring the amplitudes of the oscillatory signals derived from said baffle as it is moved; terminating movement of said baffle when the amplitudes of said signals are a minimum; and thereafter adjusting the feed rate of said charge material for optimum ion output from said source.

6. An improved ion source for a calutron unit comprising an arc chamber, means for establishing and maintaining an arc discharge in said are chamber; means for feeding a charge material vapor into said are discharge to form ions, means for extracting and accelerating said ions from said are chamber, a movable bafile in said are chamber, and means for positioning said bafiie with respect to said are discharge so that the amplitudes of oscillatory signals derived from said bafiie are minimized.

7. In an improved ion source for a calutron having an arc chamber, means for establishing and maintaining an arc discharge in said are chamber, means for feeding a charge material vapor into said are discharge to form ions and means for extracting and accelerating said ions from said are chamber; the improvement which comprises providing a movable bafile in said are chamber and means for positioning said baffle with respect to said are discharge so that the amplitudes of oscillatory signals derived from said baffie are minimized.

References Cited UNITED STATES PATENTS 2,994,800 8/1961 Lazzarini 3155.53

RALPH G. NILSON, Primzuy Examiner.

A. L. BIRCH, Assistant Examiner. 

